Indicator 2.11: Total growing stock and annual increment available for wood production

An indicator for Criterion 2: Maintenance of Productive Capacity of Forest Ecosystems

What is the indicator and why is it important?

Growing stock is a fundamental element in determining the
productive capacity of the area identified as forest available for
wood production. Knowledge of growing stock of the various
species that make up the forest and how it changes over time
is central to considerations of a sustainable supply of wood for
products and the sustainability of the overall ecosystems that
provide them.

What does the indicator show?

The Nation’s forests contain more than 800 species of trees.
Because changes in markets and technology dictate species
use for wood products, it is difficult to assign the status of
nonmerchantable to any given species except those of very
small stature or those with rare, threatened, or endangered
status. Variability in the condition of the size and quality of
these trees has considerable bearing on their value in wood
products. Generally speaking, about 94 percent of all live tree
volume on timber land in the United States is considered to be
growing stock or wood capable of being used for commercial products. The remaining 6 percent are trees of poor form, small
stature, or otherwise unsuited for wood products. Given the
minor influence of nonmerchantable volume relative to total
live volume of timber on forests available for wood production,
the remainder of the discussion for this indicator will focus on
merchantable or growing stock volume.

Overall, growing stock volume (fig. 11-1) has been rising in
all regions of the country, for the past 50 years. The exception
being the Pacific Coast and Alaska where harvesting of large
timber and losses of high-volume timber lands to reserves in
the 1970s and 1980s resulted in declines. Recent reductions in
harvest in this region have reversed this trend.

With a relatively stable base of forest land available for timber
production or timber land (Indicator 2.10) and a historic pattern
of growth exceeding removals (Indicator 2.13), the volume
of growing stock in the United States has been rising steadily
for more than 50 years. The current total of 932 billion feet of
growing stock is 51 percent higher than the volume in 1953.
U.S. conifer growing stock volume totals 529 billion cubic
feet or 57 percent of all growing stock. Conifer growing stock
volume is concentrated primarily in the West and South.
Broadleaves, at 403 billion cubic feet, account for 43 percent
of all growing stock volume in the United States. Broadleaf
volume has risen 118 percent since 1953 as second and third
growth forests of the North and South continue to mature.

Growth rates on timber land have increased on all land ownerships
(fig. 11-2). The higher rate of increase on National forests
due, in part, to a response to vigorous young stands replacing
older slower growing stands harvested in the 70s and 80s or
lost to fire. The higher overall rates and lower net change on
private lands reflects the history of these lands being the primary
source of wood production in the United States for decades.

As mentioned in other indicators in this Criterion, ownership
has a direct bearing on management policy and access to available
timber. Timber volumes are distributed unevenly among
owners because of many factors (fig. 11-3), among them history
of use, land productivity, and degree of management. As public
agencies have adjusted management policies to respond to
increasing demand for uses of public forest land for recreation,
wildlife habitat, and biodiversity conservation, the area and
corresponding volume of wood available for harvest from
public timber lands is declining and placing additional pressure
on private timber land and imports. This pressure is further
heightened by improved technologies, which allow a shift to
broadleaves, which are dominant on private timber lands, for
many uses previously dominated conifers such as paper and
composite products to meet demand. Overall, growth on private
timber land is increasing, but has slowed in response to increasing
demand caused by shifts in policy and technology and the
slowing growth of maturing broadleaf stands. This slowing
growth will likely abate slightly as regeneration following the
recent increases in harvesting gets established. The reduction of
harvest on public land is reflected in sharply rising volumes per
acre in these forests, which may create new management issues
relative to fire and overall forest health.

National forests, which account for only 19 percent of U.S. timber
land, have 30 percent of all timber volume, and 46 percent of
all conifer timber volume. Changing management policies have
significantly affected the national forests and the wood they
supply. The national forests supplied 15 percent of U.S. wood
in 1976, today they supply 2 percent. The future of wood supplies
from this source is in question, but is likely to remain low.

What has changed since 2003?

Growing stock volume increased from 856 billion to 932 billion
cubic feet (9 percent) as net growth continues to exceed
removals. Current conifer volume increased 8 percent (37
billion cubic feet) from the 492 billion cubic feet reported in
2003 and broadleaves increased 11 percent (39 billion cubic
feet) from the 364 billion cubic feet reported in 2003. Recent
large divestitures of timber lands by private corporate landowners,
particularly forest industries, have left the future of what
these lands will provide under their new ownership uncertain.
Arrangements for wood availability from these lands, ranging
for 10 to 50 years, however, were part of the forest industry
divestiture strategy.